When fluorescent lamps break, fragments of the glass tube and powders from the phosphor coating inside the lamp are scattered about. In places where food is processed or stored, and particularly in food-processing plants and lighted display cabinets in supermarkets where stocking clerks and customers handle food in proximity to the cabinet lamps, it is at least highly desirable, and is often required by government regulations, that the lamps be protected in a way that minimizes the possibility of the lamps being broken and if they do break the possibility of glass fragments and phosphor powders escaping and contaminating the food. Fluorescent lamps with protective assemblies are known and widely used for this purpose. Fluorescent lamps with protective assemblies are also desirable in industrial settings and in various places in residences, such as kitchen, shops and garages. Examples of such lamps are those described and shown in U.S. Pat. Nos. 3,453,470 (Hammer, Jul. 1, 1969); 3,602,759 (Evans, Aug. 31, 1971); 3,720,826 (Gilmore et al., Mar. 13, 1973); 3,808,495 (Win, Apr. 30, 1974); 4,048,537 (Blaisdell et al., 1977); 4,924,368 (Northrup et al., 1990); 5,173,637 (Sica, 1992); 5,536,998 (Sica, 1994); and 5,729,085 (Sica, 1998). The Sica patents are owned by the assignee of the present invention.
In most instances, the prior art protective assemblies for fluorescent lamps include special molded end fittings that fit onto the terminal caps of the lamp and hold a protective sleeve in place on the lamp. In some cases, the end fittings are intentionally designed so that they can be removed from the lamp, thus allowing the protective assembly to be reused as lamps burn out and are replaced. Removable protective assemblies do not fully ensure that glass fragments and phosphor powders are retained in case the lamp breaks, inasmuch as the removable end fitting can be dislodged from the lamp and the protective sleeve if the lamp breaks. Regardless of whether the end fittings are permanently attached to the lamp or are removable, they are relatively expensive and usually have to be designed for a specific lamp style to ensure a proper fit.
The protective assemblies of the Sica '637 and '998 patents referred to above consist of a protective tube extruded from a polycarbonate resin that is stabilized against ultraviolet radiation and a collar at each end that is shrink-fitted over the flange portion of the respective terminal cap and over an end portion of the protective sleeve. Each collar is bonded to both the terminal cap and the protective sleeve to ensure that the terminal caps, collars and protective sleeve remain intact should the glass tube of the lamp break. The protected lamp of the Sica '085 patent also has a protective tube extruded from a polycarbonate resin that is stabilized against ultraviolet radiation. Each end of the tube is formed by thermal and mechanical compression working to provide a necked down end portion. The necked down end portions are secured to the terminal caps of the fluorescent lamp by an adhesive, preferably by a double-faced contact adhesive tape. The lamps of the Sica patents provide excellent protection against breakage of the lamp, and if the lamp should break, the protective assembly provides an enclosure for the lamp glass tube and terminal caps that is secure against separation, thus preventing release and scattering of glass fragments and phosphor powders. The Sica lamps are relatively inexpensive to produce, inasmuch as they use simple tubular elements and commercially available adhesive tapes and are easily and quickly assembled.
WO 99/12186 (published Mar. 11, 1999, Sica) describes and shows curved fluorescent lamps, such as U-shaped lamps, that are protected by two-part sleeves, each part being injection-molded to a shape in plan that corresponds to the shape of the lamp and to a semi-cylindrical cross-section from a polycarbonate resin that is highly stabilized against ultraviolet radiation. Each part has a flange along each edge, and the flanges of the two parts mate and are joined by fusion bonding, chemical bonding or adhesive bonding. Each end of the protective sleeve is sealed and adhered to the terminal cap of the lamp by a shrink-fit collar and an adhesive (see Sica '637 and '998 patents referred to above) or by a thermally/mechanically formed necked down portion and an adhesive (see Sica '085 patent referred to above).
In order to fit over an entire lamp, the two parts of the protective sleeve of WO 99/12186 are of large size, thus requiring very expensive molds. Similarly, the very long lengths of the mating flanges make it difficult to join the flanges, regardless of the type of joints.